feat: add getSelectedMultichainAccount and listMultichainAccounts (#4330

)

## Explanation

This pull request adds two new methods `getSelectedMultichainAccount`,
`listMultichainAccounts` and `selectedEvmAccountChange` event. The
optional arguments are to make the changes backwards compatible when
used with evm specific controllers.

## References

Related to:
- [381](MetaMask/accounts-planning#381)
- [419](MetaMask/accounts-planning#419)

## Changelog

### `@metamask/accounts-controller`

- **<CHANGED>**: Adds two new methods `getSelectedMultichainAccount`,
`listMultichainAccounts`, and `selectedEvmAccountChange` event

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've highlighted breaking changes using the "BREAKING" category
above as appropriate

---------

Co-authored-by: Charly Chevalier <charly.chevalier@consensys.net>

packages/accounts-controller/jest.config.js

@@ -14,6 +14,8 @@ module.exports = merge(baseConfig, {
   // The display name when running multiple projects
   displayName,
 
+  coveragePathIgnorePatterns: ['./src/tests'],
+
   // An object that configures minimum threshold enforcement for coverage results
   coverageThreshold: {
     global: {